try suggestions from pytest-qt plugin

.travis.yml

@@ -42,15 +42,23 @@ before_install:
   - |
     if [ "$TRAVIS_OS_NAME" == "linux" ]; then
       sudo apt update
-      sudo apt install libdbus-1-3 libxkbcommon-x11-0 -y
+      sudo apt install xvfb herbstluftwm -y
     fi
 
 install:
+  - "export DISPLAY=:99.0"
+  - "/sbin/start-stop-daemon --start --quiet --pidfile /tmp/custom_xvfb_99.pid --make-pidfile --background --exec /usr/bin/Xvfb -- :99 -screen 0 1920x1200x24 -ac +extension GLX +render -noreset"
+  - sleep 3
   - python --version
   - python -m pip install --upgrade pip
   - python -m pip install --upgrade setuptools wheel
   - python -m pip install PySide2
+  - python -m pip install pytest-xvfb
   - python -c "from PySide2.QtWidgets import QApplication; QApplication([])"
 
+before_script:
+  - "herbstluftwm &"
+  - sleep 1
+
 script:
   - python setup.py tests